1. Field of Invention
The present invention relates to a system and method for quantitatively evaluating a tumor. More particularly, the invention involves using a piezoelectric sensor to detect the existence of, determine the dimensions of, determine the location of, identify the type of, determine the invasiveness of and/or determine the malignancy of a tumor.
2. Brief Description of the Prior Art
The key to successful treatment of cancer lies in early detection; in turn, the early detection and identification of cancerous growths is heavily dependent upon the capability of sensors and screening technologies. Currently, there are a variety of different sensors and tools used for investigating the mechanical properties of soft tissue and for imaging soft tissue.
One type of conventional soft tissue sensor uses an external force applicator for inducing displacement and an external displacement gauge for measuring resistive force.1,2 The external force applicator may be hydraulic or piezoelectric, and the external displacement gauge may be optical or piezoelectric. These sensors, however, require the extraction and destruction of tissue specimens; during operation, since the specimens must be cut to conform with and fit within the sensor. Exemplary soft tissue imaging tools include Computer Tomography (CT), Magnetic Resonance Imaging (MRI), Ultrasound (US), T-scan (TS) and Ultrasound elastography (UE).3-8 CT scans10 take 360 degree X-ray pictures and reconstructs 3D tissue structures using computer software. MRI scans11 use powerful magnetic fields and radio waves to create tissue images for diagnosis. US scans12 transmit high-frequency waves through tissue and capture the echoes to image tissue structures. TS7 measures low-level bioelectric currents to produce real-time images of electrical impedance properties of tissues. UE scans14 evaluate the echo time through tissue under a constant mechanical stress and compares it to that of the same tissue when unstressed. A tissue strain map is then obtained, from which an image of 2D elastic modulus distribution is created by conventional inversion techniques.
Tactile imaging12 tools, such as mammography, use array pressure sensors to probe spatial tissue stiffness variations. Currently, mammography is used in breast cancer screening to detect abnormal tissue by tissue density contrast. Mammography is the only FDA approved breast cancer screening technique, which has a typical sensitivity of 85% that decreases to 65% in radiodense breasts.9 However, in these screening processes there is a high incidence of false positives. In fact, only about 15-30% of breast biopsies yield a diagnosis of malignancy. Although effective for screening women over 40, mammography is not as effective for screening women who have dense breast tissue. Additionally, mammography and other tactile imaging tools do not have the ability to probe tumor interface properties.
Since many tissues harboring abnormal growths are stiffer than the surrounding normal tissues under compression, detecting a change in tissue stiffness has increasingly become an important factor in detection and diagnosis of abnormal tissue. For example, breast cancers are calcified tissues that are known to be more than seven times stiffer than normal breast tissue.10-13 Similarly, plaque-lined blood vessels are also stiffer than normal, healthy blood vessels.
U.S. Pat. No. 7,497,133 discloses a piezoelectric finger sensor that may be used to detect tumors by measuring tissue stiffness. Tumor mobility was assessed from the ratio of the shear modulus to the elastic modulus (G/E) ratio of the tumor or by sensitive direct tumor mobility measurement using two piezoelectric finger sensors, one for pushing and one for measuring the movement of the tumor that results from the pushing. The patent concludes that the G/E ratio is higher in a tumor region than the G/E ratio for surrounding normal tissue and that a much higher G/E ratio in the cancer region indicated that the tumor was less mobile under shear than under compression, as compared to the surrounding normal tissue. Although the patent concludes that these measurements may offer the potential for non-invasive breast cancer malignancy screening, it does not disclose a method for determining malignancy, invasiveness or tumor type.
Consequently, there remains an important need to accurately and non-invasively detect and identify tumors. Moreover, there exists a need to develop a means for probing tumor stiffness to determine the type, malignancy and/or invasiveness of the tumor.